Topic: My second Nighthawk is a nightmare

[dudeman750]

Hi yall,
I owned a 1984 CB550SC back in the 90's. I bought it with 2000 miles on it for $500. It ripped, I could hit 65 in 60 feet and easily over 100 in a couple of blocks.

Well I recently bought a 1982 CB650SC for 500 and it has 14k miles on it. I have the classic high RPM BOG syndrome after pulling and cleaning the carbs. I do not have the air vent hoses attached anymore as they fell apart during my cleaning of them. I wouldnt think they would matter much, more for EPA as a fuel vapor vent back into the motor. Well it wont rev over 5k under load but pulls good up to 5k. What is it with these carbs? I have checked evything else. I feel the problem is the carbs.

Can anyone help? I dont want to put a  lot of money in this bike as it aint worth more than 300 bucks blue book. I did a lot of cosmetic cleaning on it, and it works great, as long as you dont want anything over 5k RPM. My old bike didnt really perform UNTIL 5K so I think I am missing a lot of fun up there. I do realize the old one was a DOHC vs this SOHC. Can anyone suggest anything? should I try to rebuild the carbs? or just start throwing a smaller main jet at it? I have read many posts, and am at a loss as to which direction to go. Please help O Jap guru honda dudes !!!!. I am familiar with carbs in general have a lot of time building 2 stroke twins, (jetski's). This thing has me befuddled. These CV carbs operate on self generated vacuum? I eliminated all the vacuum lines and plugged the one vacuum hole in the number 2 or 3 carb with a screw. Also the accelerator seems to work, but sprays kinda weak. The problem is WOT, it just dosent run. Low and mid seem ok. I have seen a crapload of similar posts, with no definative solution.
I eliminated the vacuum operated fuel valve right away, and installed an inline filter. The only thing not stock is the abscense of the fuel vapor port vaccuum lines. I would not think they would be involved with the fuel metering at all.

[TwoTired]

Wouldn't it be nice to know it the engine was getting too little fuel or too much fuel above 5K?

The spark plug deposits would tell you. if you knew hor the read them.

http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

A restrictive air filter will hinder breathing/ air flow.  Remove it for a test run.  Better? Worse?

A restrictive fuel line/filter will hinder high speed fuel flow.  Remove the end at the carbs and point it at a quart jar.  Time how long it take to fill it.

Cheers,

[dudeman750]

Im pretty sure its the running rich problem. my plugs look kinda dark.

[tomkimberly]

Be glad you have an 82' as the slow jet is replaceable.

I have an 81' and it took me two years to get it to run right. After removing and cleaning the carbs at least a dozen times I finally gave up on them and found a set from a 82' CB650. This did not solve the problem completly but was a good start. Seems one of the previous owners of the bike these 82' carbs came off of cleaned the cross holes in the slow jets and managed to open them up to large. Honda still has these (at $7.38 each) so I replaced them. THis was a big improvment however the bike still did not want to run at WOT. I checked all the normal items again and again (timing, valve clearance, fuel supply, charging voltage, battery condition, etc.) and all were in spec. I finially in frustration changed out the plug wires and and bought new plug caps. What a difference! This bike now rocks and runs better than new.

That's my story and I'm sticking to it. So those of you with CB650's, it is not just one thing, it is a combination of several small ones that need to be addressed.

Tom

[dudeman750]

I have checked static timing, valve clearance, eliminated the fuel valve completely, battery holds up even after extended sitting time so I think my charging system is fine, with so small a battery. I did install an inline filter but the inlet and outlet are the same or bigger than the vacuum operated valve I took out. The plug wires and caps look to be aftermarket 8mm high temp and seem to be in ok shape, with only a couple grooves in the insulation where they touch the head fins. From the way the coils are mounted, it seems you cant avoid contact with the heads. Someone told me coils could cause this problem, but it runs just fine up to 5k to 7krpm. I havent turned around while riding to see if any smoke but at idle all pipes are hot and all 4 seem to be firing. My #1 was popping a little back through the carb, but I think the valves were not closing fully, took care of that when I adjusted valves last weekend. Gonna try no air filter next, but I think I ran it with no airbox at all initially and had same problem. Timing advance turns easily by hand, I lubed it thouroghly. Been through a lot of posts here for same type problem.

[tomkimberly]

Did you poke a wire thru the slow jets when you clean them? If so, they are more than likely too large now and will cause a rich condition that can only be solved by new ones.

Also new wires and caps are a low buck solution, new 7MM wire can be had a any NAPA dealer and new NGK caps can be found at most motorcycle shops. BTW, if you replace the caps and wires, also use new plugs as your old ones are most likely carboned up from running too rich.


Tom

[dudeman750]

Yes, I did poke a guitar string through only one of them that was clogged. I used a .009" string. I have been reading about the cross holes on the low jets, mine are all open. (I figured they should be? as they look to be cross drilled?). I will go hunt wires and caps. I dont even have a spark plug wrench that will allow me to take out the 2 and 3 plugs, I can only get out 1 and 4 with a deep well 18mm socket. What a crappy design. My wires look good, buy I will replace anyway. So I assume people go buy generic wires and hook them up to the coil with those crimped things in the coil? and then get the screw on caps? these I have are permanent caps. Or buy a 4 cylinder wire set for a car and cut them down and attach to the crimp piece that slides into the coil?

[tomkimberly]

Your coils should have screw on caps for the plug wires and no splicing is required.

Go to Sears and purchase a deep 18MM socket. With just a little grinding, it will work on # 2 and # 3 (you will want to remove the tach feed housing to get to  the # 3 plug).

I strongly recommend you purchase new slow jets.

Tom

[mlinder]

The 18mm I got from Schucks auto fits. You have to drop it in to 2 and 3 first, but then you can attach your ratchet.

[dudeman750]

Think its fixed. It was the coil wires. I guess moisture had invaded the front 2 holes in the coils and completely corroded the terminals. I cleaned that up, did some creative taping of the wires, ( I have now found out I have Dyna 2.2 ohm coils and Dyna 800 wires) and IT RUNS STRONGLY TO REDLINE! Still loads up at idle, but driveability is much better and power is much what it should be. This winter I plan on doing a proper rebuild of the carbs and paint the tank and covers. My new master cylinder should be here tomorrow, so I hope I can put some miles on soon. Thank god I found this forum. And thanks for all of you experts to answer noobie questions.

[tomkimberly]

Great news! I'm glad it was something simple.

Remember guys with 81' 650's, it is a combination of many small problems that need to be adressed but these bikes can be made to run again!

Tom

[dudeman750]

It's running ok..... very wierd, you can let it idle for 5 mins, no problem, if you slowly open the throttle, it will rev. If you snap open once it bogs. If you snap repeatedly it cleans out and revs good. If you ride, its ok, but some hesitation at the low to high rpm transition point. Guess I should run some gas/cleaner through it. Only about 28 miles so far since carb half ass cleaning. I put some seafoam in the tank. My best guess is its lean at low RPM and Rich at WOT. Go figure? I found a pic of my first bike today. Made me feel nostalgic... here it is